The IEEE 802.11a standard employs orthogonal frequency division multiplexing (OFDM) using 20 megahertz (MHz) wide channels and specifies an accuracy of 20 parts-per-million (PPM). Oscillators with an accuracy level of 20 PPM are sufficient for the IEEE 802.11a standard in the 5 gigahertz (GHz) radio frequency (RF) band.
Two different wireless standards are considering using OFDM with 10 MHz channels, including the IEEE 802.11j standard for use in Japan and the DSRC standardization (Dedicated Short Range Communications). DSRC is a communications approach to allowing short range communications between vehicles and the roadside for a variety of purposes, such as electronic toll collection, intersection collision avoidance, transit or emergency vehicle signal priority, electronic parking payments, and commercial vehicle clearance and safety inspections. IEEE 802.11j (or, “11j”) and DSRC have both described achieving OFDM with 10 MHz channels by using a clock at one-half the rate the 802.11a OFDM clock, or 10 MHz kernel sampling, and 10 PPM oscillators. In order to keep the 10 MHz OFDM oscillator-offset performance equal to the 20 MHz 802.11a, the standards committees of both 11j and DSRC have recommended using 10 PPM oscillators.